Continuity mistake: At the big dinner, the Grandma tries to show the Japanese man some pictures and he shakes his head as he eats his green soup. A minute later, they serve the green soup.
Continuity mistake: During the beach party, when Mandy Moore's character is singing, her friends, who are supposed to be her backup singers, don't sing along with her. They somehow manage to sing the whole song without moving their mouths.
Continuity mistake: Just before the Princess goes to smash her ice cream cone into the cheerleader's chest, she takes a bite off the top of the ice cream, but when she pushes it towards the camera you can see that it hasn't been eaten at all.
Continuity mistake: When Mia at the end hits the ball and it hits Josh, there are two shots in which he is kneeled over in pain with the ball nowhere in sight. then, as she jumps over him, the ball suddenly appears a foot away from him.
Continuity mistake: When Mia is going to see Michael about her "baby", the band finishes and the main singer walks off, followed by two girls carrying equipment. In the next shot, the guy is standing back where they performed, having just finished singing, talking to the girls.
Other mistake: At the end of the movie, when Mia is observing her new palace, the Genovian flag is fluttering on its top. But as the plane circles, the angle of the flag should change, but it doesn't. Obviously a CGI error.
Continuity mistake: Right at the start of the movie, when Mia is shown opening her window blinds, there are some books on a shelf to the left. The lowermost is Jane Austen's "Pride and Prejudice", which her grandmother will first give her much later in the movie, together with a rather large book ("The Vanderbilt Complete Book of Etiquette"), in which Mia has already been reading in the immediately preceding scene.
Continuity mistake: When Mia and Michael are talking and Michael asks Mia to come and see his band, keep your eye on the background. You see Lily running to catch up with them and she passes in between two people and doesn't even look at them, then in the next shot she passes them again, points at the boy who has stepped to the side and says "Not you, I don't even know you."
Continuity mistake: When Josh is finished making his speech, everyone starts cheering; you can see in the background the guy banging on the drum is beating it much faster than he is when the camera gets a close-up of him.